Method of manufacture of smokeless powder



Patented Mar. 29, 193$ UNM'ED ,iast

METHOD OF MANUFACTURE 10F SMOKE- LESS POWDER No Drawing. ApplicationApril 3, 1936, Serial No. 72,563

8 Claims. (01. 52-20) This invention relates to an improved method ofmanufacture of smokeless powder, and more specifically to an improvedmethod of manufacture of colloided smokeless powder.

Colloided smokeless powder, also called dense smokeless powder, isusually made from nitrocellulose colloided by a volatile or non-volatilesolvent therefor, or by a mixture of volatile and non-volatile solvents.The colloided mixture of nitrocellulose and solvent or solvents ispressed into strands, which are cut into short sections known as grains.The grains are treated for removal of solvent and moisture, dried,glazed, etc. Such colloided or dense smokeless powders may,

' or may not, contain nitroglycerin.

powder may be subjected for solvent removal and drying, the apparatusrequired, and the percentage of solvent recovered, are important factorsin the ultimate cost of the powder.

Heretofore, various methods have been used for removing the solvent fromthe grains of dense smokeless powder. In one process, known as waterdrying, the powder grains are soaked in hot water, into which thesolvent diffuses. The powder grains are removed from the water and driedin acurrent of hot air, to remove the adhering moisture. This process ismost frequently used in the case of large grains of smokeless powder forlarge caliber guns.

The process most frequently used for drying relatively small grains ofpowder for small caliber guns is known as air drying. The cut grains,containing solvent, are exposed on shallow trays in large dry houses toa current of warm air for a long period of time. The warm air slowlyremoves the solvent as vapor in such a dilute form that economicalrecovery of the solvent is impossible.

Solvent recovery, without the complete drying of the grains of smokelesspowder, has heretofore been accomplished by placing the cut grains ofpowder containing solvent in a closed container. Warm air is circulatedthrough the powder and passes through a condenser, kept cold bysuitablerefrigeration exterior to the powder container. The air current carriesthe solvent vapor to the condenser, where the solvent is condensed to aliquid form and is collected and removed for re-use. The air detrainedfrom solvent vapor is heated up to a point at which it is capable ofreabsorbing more solvent and is again passed through the powder grains.This cycle may be repeated indefinitely. In such a process, solvent isrecovered, but the powder grains must subsequently be removed from thecontainer for final drying.

Processes for solvent removal and drying of smokeless powder haveheretofore required from three to five days and large dry houseinstallations. Large quantities of powder are exposed to the risk offire in the dry houses. The passage of, warm air through smokelesspowder grains generates static electricity, the discharge of which mayignite the powder dust attendant to such operations. The equipment ofdry houses usually consists of wooden trays for holding the powdergrains during the drying process. Metal trays are undesirable, becauseof the possibility of friction. Wooden trays are unsatisfactory, due tothe possible contamination of the powder from wood splinters. Splintersare difiicult to screen from the powder, and cause trouble in themachines used for loading the smokeless powder into shells. The usualdry houses are more or less hazardous to the workmen, as it is necessaryto enter them from time to time to re-arrange the trays or to fill orempty the trays. Attempts to speed up the rate of drying in such dryhouses by raising the temperature or increasing the air velocity havenot been successful. Such changes result in caking the grains together,in distortion of the individual grains, and in surface hardening of thegrains, which closes the pores and materially retards the removal of thesolvent or contained moisture.

To my surprise, I have found that the passage of a mixture of steam anda fixed gas, preferably an inert gas, such as nitrogen or carbondioxide, althoughair may be used, through the body of smokeless powdergrains containing solvent, results in the very rapid removal of thesolvent from the powder grains without the attendant disadvantages ofdistortion of the grains, surface hardening thereof or caking togetherof the grains. The solvent can be removed from the grains so treated,and the powder dried completely by the use of air for this finaloperation, within a period of time of from one to three hours,approximately, as compared to approximately five days heretoforerequired, and without the disadvantages recited above, attendant totheolder methods.

Instead of steam, I may use the vapors of a light petroleum hydrocarbon,such as gasoline, or the vapors of carbon tetrachloride, or the vaporsof other volatile liquids which have no solvent action upon the powdergrains. I have found that the vapors of coal tar hydrocarbons, such asbenzene, toluene or xylene, are unsuitable, for the reason that suchvapors in themselves or in combination with the solvents in thesmokeless powder, exert a solvent action on the powder grains and causesoftening and caking of the grains. However, I prefer to use steam andair for the sake of economy and for simplicity in the subsequentrecovery of the solvent or solvents.

A further advantage of my improved process lies in the increasedstability of powders so dried, for the reason that I subject powders inmy process to a relatively moderate temperature for only a short period,and it is well known that the longer a. smokeless powder is subjected toan elevated temperature the greater its degree of decomposition and thelower its stability test.

A further advantage of my process is that, due to the greater uniformityof the shape of the grains of smokeless powder produced by my improvedmethod of drying, because of the more uniform removal of solventtherefrom and less distortion I obtain with a given charge of powder ina given gun a lower breech pressure than has heretofore been possible.by methods of solvent removal and drying used heretofore.

In my improved process I pass a mixture of steam and air or other flxedgas inert to the powder through the grains of solvent-containingsmokeless powder in such a manner as to raise the temperature of thepowder rapidly to a point near 100 C. in a few minutes, and then passair or other fixed gas inert to the powder, through the same powder fora relatively longer time while again raising the temperature graduallyto about 30-95"' C.

In a typical example of the carrying out of my process, using 107.5 lbs.of a. 22 caliber double-base smokeless powder containing solvent, I passsteam and air through the powder as follows:

Inlet Outlet lbs. per sq. Time a 0 p inch above min.

atmospheric or a total time of steam-air treatment under the abovetemperature conditions of 19 minutes.

I then give the same powder an air drying treatment to remove themoisture left in. the powder by the steam, as follows:

Inlet Outlet n per Time 1 6 5 3 inch above min.

atmospheric or a total time of drying treatment under the aboveconditions of 75 minutes, so that, in the above example, the combinedtime of total treatment is 94 minutes. Such treatment reduced the totalvolatile content of the powder grains to 0.22%.

While, in the above example, a pressure of 2 to 4% lbs. is shown in thetreatment, this is in no way limiting, and I may use any suitable temperature and pressure adapted to the grain size of the powder beingtreated. I may use atmospheric pressure, although it is preferable, forconvenience, to use pressures slightly above atmospheric in the closedpowder container, in order to carry out the vapors.

In the above example, my finished, dried smokeless powder had thefollowing composition and characteristics:

Nitrocellulose percent 83.29

A smokeless powder made from the same mix, but dried in the prior artway, hada com- In addition to the much shorter time of treatment,already mentioned as an advantage of my improved process, it will benoted by comparison of the above tables that a further improve-- mentresides in the lower moisture content (0.30 vs. 0.66%), a higher Tallanitest (208 hours vs. 189 hours) and an improved surveillance test (53days vs. 45 days).

In the above example, there was recovery of 7.17 lbs. of alcohol and2.08 lbs. of acetone, all of .which would have been lost in the priorart, hot air dry-house method.

In a further example of the carrying out of my improved process ofdrying smokeless powa sample of .22 caliber powder, was steamair driedas in the foregoing example, then coated with 3% of di-ethyl phthalateto make a progressive-burning powder. This, with a charge of 2.26grains, gave a pressure of 18,000 lbs., and a velocity of 1301foot/seconds, as compared to prior art powder having a charge of 2.56grains and giving a pressure of 18,400 lbs.,.and a velocity of 1309foot/seconds. Thus my improved powder required a lower weight of chargeand a lower pressure to give essentially, within experimental error, thesame velocity.

A further advantage of my improved drying process is, that such allowsthe use of an excess of deterrent solvent on the powder in the coatingoperation, with subsequent recovery of the solvent, instead ofeconomizing in deterrent solposition and characteristics as follows:Nitrocellulose pe'rcent 83.39

\ Nltroglycerin do 14.79

Diphenylamine 'do.. .63 Potassium nitrate do .41 Unaccounted for do .12Moisture do .66 Taliani test hours 189 Surveillance test 775 C. ..days45 vent by using only suillcient of the deterrent by the use of anexcess of deterrent solvent, to 100 lbs. of .22 caliber smokeless powderI added 4 lbs. of di-ethyl phthalate in solution in 20.5

. cient to merely wet the powder grains, (a solu- "der grains), andleaves deterrent solution collected at the base of the vessel, theentire mass of smokeless powder and deterrent solution is placed in mydrier, and a mixture of steam and air at a temperature of 60 C. at theinlet, 56 C. at the outlet thereof, under a pressure of 3 lbs., passedthrough for a time of 10 minutes. Then a mixture of steam and air at atemperature of 79 C. at the inlet, and 75 C. at the outlet, is passed inat a pressure of 3 lbs. for a period of 5 minutes. Then air ata.temperature of 60 C., and an outlet temperature of 55 C. under apressure of 4 lbs., is passed through the smokeless powder for a periodof 180 minutes. The vapors escaping from the outlet of mytreatment'chamher are passed to a condenser, and all alcohol possiblerecovered therefrom by condensation.

- After the above treatment the smokeless powder contained about 30%moisture. To show the ballistics of smokeless powders treated by theabove process, and by the coating process heretofore used, I give belowa table:

A substantial advantage resulting from my above treatment. of smokelesspowder with the deterrent in excess of'dilute alcohol solution, is

' that there is no sticking together and clustering of the smokelesspowder grains, a disadvantage encountered heretofore in old processeswhen the deterrent was carried by 95% alcohol.

I do not limit my process to the treatment of any particular variety ofsmokeless powder, and I may use my process in the solvent removal anddrying of single or double-base powders of any size or shape ofgranulation. The time taken by my solvent removal and drying treatmentwill naturally vary with size or shape of the powder grain, since thelarger grains will require a longer time for removal of solvent thanwill the finer grains. I do not limit my temperatures to those shown inthe examples, since I may wish to subject certain powders to a longertime of treatment at somewhat lower temperatures, and other ppwders toa' shorter treatment at somewhat higher temperatures. I may treat by myimproved process the so-called deterred or progressive-burning powders,'i. e., those coated with a deterrent, for example dinitrotoluol,di-ethyi phthalate, and the like.

My improved solvent removal and drying proccss may be carried out in anysuitable form or apparatus in which undried powder grains are subjectedto a'current of air and water vapor or steam. Such apparatus may consistof a column containing the powder, a tank, a box, or any containerthrough which can be passed the steam/air current which accomplishes thesolvent removal and drying.

What I claim and desire to protect by Letters Patent is:

1. In a method of removing solvent from smokeless powder, the stepcomprising subjecting smokeless powder to the action of a rapid currentof a fixed gas and a vapor of a volatile liquid having no solvent actionupon smokeless powder.

2. In a method of removing solvent from smokeless powder, the stepcomprising subjecting smokeless powder to the action of a rapid currentof a fixed gas and a vapor of a volatile liquid having no solvent actionon smokeless powder at an elevated temperature.

3. In a method of removing solvent from,

smokeless powder, the step comprising subjecting smokeless powder to theaction of a rapid current of air and a vapor of a volatile liquid havingno solvent action on smokeless powder.

4. In a method of removing solvent from smokeless powderIthe stepcomprising subjecting smokeless powder to the action of a current ofnitrogen and a vapor o'f a volatile liquid having no solvent action onsmokeless powder.

5. In a method of removing solvent from smokeless powder, the stepcomprising subjecting smokeless powder to the action of a current ofcarbon dioxide and a vapor of a volatile liquid having no solvent actionon smokeless powder.

6. In a method of removing solvent from smokeless powder, the stepcomprising subjecting smokeless powder to the action of a rapid currentof a fixed gas and water vapor.

7. In a method of removing solvent from smokeless powder, the stepcomprising subject- BERNHART TROXLER.

